The invention relates to an AC-DC converter comprising a three-phase input, designed to be connected to an AC power system having a first fundamental period, a DC output, and a first rectifier circuit connected between said input and said output.
Known converters often comprise three-phase rectifiers with diodes connected to the AC power system and a DC voltage smoothing capacitor connected on output of the rectifier. However this type of converter produces very high harmonic currents on the power system. These harmonic currents generate a high distortion ratio even with input filtering inductors.
To limit the harmonic current ratio, it is known to use controlled chopper transistor rectifiers to take a sine wave current from the power system. However such a converter is very costly and complex. Moreover, the DC output voltage is very high for regulation of the input current. This has the consequence of using overdimensioned components having high voltage withstands.
Other solutions consist in combining diode-based rectifiers with a chopper. However, in such combinations the current flowing in the diodes has a very high frequency. It is compulsory for this type of converters to have high-speed diodes. These diodes also have to be overdimensioned for large current peaks to be able to pass at each chopper pulse. Furthermore, a high frequency filter is necessary to eliminate the chopper frequency.
The solutions proposed in the state of the art are not able to be applied to already installed converters. Compliance with stray disturbance standards then requires total replacement of converters of known type.